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<p>A significant vulnerability affecting AMD processors has recently come to light, potentially exposing millions of devices powered by these chips to potential cyberattacks. Researchers from Google have uncovered a major security flaw, identified as “EntrySign,” which affects AMD’s Zen 1 through Zen 4 processors. The flaw allows attackers to push malicious microcode updates to compromised devices, potentially enabling them to hijack the system.</p>



<p>This blog post delves into the details of the vulnerability, how it works, and the potential risks associated with it. We will also explore how this issue affects not only users of AMD-powered systems but also the wider cybersecurity landscape. Furthermore, we’ll look at the steps that users and organizations can take to protect themselves from this growing threat.</p>



<p>What is the EntrySign Vulnerability?</p>



<p>The vulnerability, dubbed EntrySign by the researchers at Google, specifically involves the AES-CMAC (Advanced Encryption Standard &#8211; Cipher-based Message Authentication Code) hash function, which AMD uses in its processor’s signature verification process. The issue stems from a cryptographic error, as AES-CMAC is primarily designed as a message authentication code rather than a full-fledged hash function.</p>



<p>This flaw allows attackers to manipulate the signature verification mechanism, potentially enabling them to push unauthorized microcode updates onto affected systems. Essentially, an attacker could exploit this vulnerability to install malicious firmware, giving them the ability to control the system and execute arbitrary code at the hardware level.</p>



<p>CVE-2024-56161: A High-Risk Vulnerability</p>



<p>The vulnerability has been officially tracked as CVE-2024-56161 and has been assigned a severity score of 7.2 out of 10, classifying it as a high-severity vulnerability. While the flaw is not considered an immediate, critical threat (such as those with a 10/10 rating), its potential consequences make it a major concern for both individual users and organizations that rely on AMD processors in their devices.</p>



<p>The severity of this vulnerability is due to the low-level access that could be gained by threat actors. Gaining control over a processor’s microcode could allow attackers to bypass traditional security defenses such as OS-level protections, potentially enabling them to carry out persistent attacks that are difficult to detect and mitigate.</p>



<p>Impact on AMD Zen Processors</p>



<p>The EntrySign vulnerability affects AMD processors from Zen 1 through Zen 4, which includes a significant portion of the company’s processor lineup. These chips are used in a wide variety of devices, including personal computers, laptops, and servers, meaning the impact could be widespread.</p>



<p>• Zen 1: The first generation of AMD’s Ryzen processors, launched in 2017, and used in many consumer desktops and laptops.</p>



<p>• Zen 2: The next generation of Ryzen processors, launched in 2019, offering significant performance improvements over Zen 1.</p>



<p>• Zen 3: Launched in 2020, Zen 3 processors, including Ryzen 5000 series chips, brought even greater performance and efficiency.</p>



<p>• Zen 4: The latest generation, launched in 2022, with significant performance boosts, especially in terms of energy efficiency and multi-core performance.</p>



<p>While these processors are all affected, it’s important to note that the Zen 1 and Zen 2 chips are more likely to be in older systems, which may not be patched or updated as regularly as newer systems. However, the vulnerability also affects Zen 3 and Zen 4, which are still in active use today.</p>



<p>How Attackers Could Exploit the Vulnerability</p>



<p>In theory, an attacker could exploit this vulnerability in several ways. Most notably, by using it to push malicious microcode updates to an affected system. Microcode is a set of low-level instructions that processors use to execute machine-level instructions. Microcode updates are often used by manufacturers like AMD to fix bugs or enhance performance, making them a trusted mechanism in the system’s operation.</p>



<p>An attacker could manipulate this trust by exploiting the EntrySign vulnerability. If they can deliver malicious microcode to a device, they could potentially gain full control of the system. This would give them the ability to:</p>



<p>1. Hijack the system at the hardware level, bypassing OS and security software.</p>



<p>2. Install backdoors or other types of malicious software that persist even after rebooting the device.</p>



<p>3. Steal sensitive information or use the compromised machine in a botnet for further attacks.</p>



<p>Such attacks would be hard to detect because they would take place at the processor level, below the operating system and application layers. As a result, traditional security software would likely miss these threats.</p>



<p>Google’s Response: Jailbreaking the Device</p>



<p>To help users and researchers understand and mitigate the vulnerability, Google’s security team has released a tool that allows users to install the necessary microcode updates to protect their systems from exploitation. This tool can be used to “jailbreak” affected devices and apply the updates directly, thus mitigating the threat posed by the vulnerability.</p>



<p>While this is a helpful solution for technically savvy users, it is not a comprehensive fix for the average consumer. It’s also important to note that not all devices will be able to apply these updates right away, especially if the manufacturer (in this case, AMD) does not release a formal patch to address the vulnerability.</p>



<p>What Can Users Do to Protect Themselves?</p>



<p>Given the severity of this vulnerability, it’s crucial for users to take steps to protect their devices. Here are some actions you can take:</p>



<p>1. Monitor for updates from AMD: Keep an eye on AMD’s official channels for any security patches or microcode updates related to CVE-2024-56161. AMD is likely working on a formal fix for this vulnerability.</p>



<p>2. Update your firmware: Ensure that your system’s firmware (BIOS/UEFI) is up-to-date, as manufacturers may include fixes for known vulnerabilities in these updates.</p>



<p>3. Use Google’s jailbreak tool cautiously: While Google’s tool can help mitigate the issue, it’s intended for advanced users. Regular users should wait for official fixes from AMD or their device manufacturer.</p>



<p>4. Enable Secure Boot and TPM: Enabling Secure Boot and ensuring Trusted Platform Module (TPM) functionality is activated can provide some additional protection against low-level exploits.</p>



<p>5. Consult with your IT team: If you manage enterprise systems with AMD processors, consult with your IT team or a cybersecurity expert to assess the risk and develop a mitigation plan.</p>



<p>Conclusion: A Wake-Up Call for Cybersecurity</p>



<p>The discovery of the EntrySign vulnerability highlights a crucial aspect of modern cybersecurity: even the most trusted hardware components can have vulnerabilities that leave users and organizations exposed. While AMD processors are generally considered secure, this cryptographic flaw has the potential to undermine the integrity of affected systems and provide attackers with an unprecedented level of control.</p>



<p>For users, this serves as a reminder of the importance of keeping their systems up to date and remaining vigilant about potential threats. As for AMD, the company will need to act swiftly to issue an official patch to prevent further exploitation of this flaw.</p>

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